A color light-sensitive material is subjected to processing at the steps of color developing, desilvering, rinsing, and stabilizing after exposing. There are used a color developing solution for color developing, a bleaching solution, a bleach-fixing solution and a fixing solution for desilvering, city water or ion-exchanged water for rinsing, and a stabilizing solution for stabilizing, respectively. The respective processing solutions are usually adjusted to a temperature of 20.degree. to 50.degree. C., and the light-sensitive material is dipped in these processing solutions and processed.
Of the above processing steps, the color developing and desilvering processings are basic. At the color developing step, a developing agent, which is a reducing agent, acts on exposed silver halide grains contained in the light-sensitive material to reduce Ag.sup.+ to Ag, and at the same time, an oxidation product of a developing agent is reacted with a coupler to form a dye image corresponding to a silver image. At the subsequent desilvering step, silver formed by the development is oxidized by a bleaching agent, which is an oxidizing agent, to convert it to silver halide, which is dissolved and removed with a fixing agent, which is a silver halide solvent, whereby only the dye image is formed.
This desilvering step includes a bleaching step and fixing step. There is available a method in which these steps are carried out in the same bath or different baths, and a method in which the bleaching step and bleach-fixing step are carried out in different baths.
Accordingly, the bleach-fixing step in which the bleaching step and fixing step are carried out in the same bath is used in various modes at the processing step of the color light-sensitive material. In particular, in a light-sensitive material which is relatively susceptible to desilvering, such as a color paper, a method in which only the bleach-fixing step is carried out as the desilvering step is applied in many cases. In the processing in which only the bleach-fixing step is carried out as the desilvering step, the number of the processing baths can be decreased, and has an advantage that a replenishing solution can be decreased, since only one kind of the replenishing solution is used. In addition, compared with the case in which both the bleaching solution and fixing solution are used, the problem that the solutions are mistakenly charged does not arise, and therefore, this is more suited to processing by unskilled persons.
There can be given as a bleaching agent contained in such a bleach-fixing solution, a ferric complex, such as aminopolycarboxylic acid, aminopolyphosphonic acid, and the salts thereof. To be representative, a ferric ethylenediaminetetraacetate complex salt is widely used. In addition thereto, a ferric 1,3-diaminopropanetetracetate complex salt is available as a bleaching agent having a high oxidizing power. Meanwhile, thiosulfate is available as a fixing agent.
Accordingly, in such a bleach-fixing solution, an iron (II) salt and a silver complex ion are accumulated as the processing proceeds, so that the activity thereof is lowered.
In addition, a fixing agent and a preservative contained in a bleach-fixing solution are susceptible to air oxidation by aging while the solution is not used for processing a light-sensitive material. These agents are decomposed to generate a sulfurization, so that a problem, such as a stain on a surface of the light-sensitive material, is caused.
In order to prevent such reduction of activity and the afore-mentioned problem, there is employed a method in which a suitable amount of a replenishing solution is added to a bleach-fixing solution and an old solution is discharged as an overflow. However, the increase in the replenishing amount results in an increase in the amounts of agents and water employed. This is not preferable from the viewpoint of saving the resources and the reduction of a waste water amount, which are intensively required in recent years from the standpoint of environmental maintenance. In addition, it is disadvantageous in terms of cost.
Further, in order to recover an oxidizing power, there is employed, for example, a method in which a bleach-fixing solution is subjected to aeration to increase an oxidation-reduction potential of the solution.
However, the application of such a method generates a foam in the solution, which results in causing problems, such as stain on the surroundings caused by the solution spilling over from a bleach-fixing bath and stain of the processing solution contained in a preceding bath by splashing into the preceding bath due to foaming. In particular, the processing solution contained in the preceding bath is a color developing solution in many cases, and therefore, the color developing solution is deteriorated. Thus, the developing power is reduced, which in turn results in causing a serious problem. In addition, there is involved another problem in that a fixing agent and a preservative are decomposed by aeration to deteriorate the fixing power.
Meanwhile, there can be given as a method for recovering a processing performance of a fixing solution, an electrolysis method in which silver is deposited on a cathode of an electrolysis equipment, and the short components are replenished to the solution after removing silver for reuse. However, the application of this method to a bleach-fixing solution causes a complicated reaction, and therefore regeneration does not necessarily go well.
Under such circumstances, there has been proposed a method in which an anion exchange membrane is applied for electrolysis to maintain and recover the processing performance of the processing solution [JP-A-3-273237 (the term "JP-A" as used herein means an unexamined published Japanese patent application)].
However, the direct application of the above method creates a problem since a bleach-fixing solution contains a bleaching agent, being a component in which the performance can be recovered by oxidation, and a fixing agent, being a component in which the performance can be recovered in a reduction condition. Accordingly, various improvements are required.
The recovery of silver is generally carried out in order to recover the performance of the fixing solution, and this method can be applied to a bleach-fixing solution.
Examples of such methods for recovering silver include:
1) a method (a metal substitution method) in which metal having an ionization tendency larger than that of silver is contacted to the solution;
2) a method (a settling method) in which a reagent for forming an inactive silver salt is added and a reduction settling method is used;
3) a method (an ion exchange method) in which an ion exchange resin is used; and
4) a method (an electrolysis method) in which silver is deposited on a cathode of an electrolysis equipment. The details on these methods are described in "Present Status of Silver Recovery in Motion-Picture Laboratories" written by M. L. Schreibe, J. SMPTE, 74, pp. 504 to 514 (1965).
Meanwhile, methods available for recovering the oxidizing power of a bleaching agent include: 1) a method in which an oxidizing agent is added (for example, U.S. Pat. Nos. 3,615,507 and 3,767,401, and German Patent Application (OLS) 2149314);
2) a method involving the contacting of oxygen (air) (for example, U.S. Pat. Nos. 3,634,088 and 3,700,450, and German Patent Application (OLS) 2113651); and
3) an electrolytic oxidation method (for example, JP-A-48-18191).
Of the above methods, the electrolysis method is paid attention to as a method for recovering both the bleaching power and fixing power of the bleach-fixing solution. However, where this method is applied, an iron (III) complex, which is an oxidizing agent, is reduced to an iron (II) complex before a silver complex ion is reduced to silver. Thus, when a bleach-fixing solution is prepared, the oxidizing power thereof is lowered, or silver is reoxidized in the presence of the iron (III) complex. Accordingly, an electrode reaction does not necessarily go on in a favorable direction in terms of the recovery of the processing performance, and a complicated reaction takes place, which makes this method rather impractical.
From such a point of view, there is disclosed in JP-B-57-16345 (the term "JP-B" as used herewith means an examined Japanese patent publication), a method in which a carbon fiber is used for an anode alone or together with other materials for an anode, and gas containing oxygen, such as air, is blown in a vicinity of the anode to electrolytically regenerate the bleach-fixing solution.
In this method, the oxidizing power of a bleaching agent is recovered not only by electrolytic oxidation but also by blowing air. If the electrolysis method is applied not only to the oxidation of an iron (III) ion, but also to the recovery of silver, the reduction of the iron (III) ion, as well as the reduction of a silver complex ion, takes place at a reduction step. While a large oxidizing power is needed for the anode, it is said that the anode provided with a large oxidizing power can improve the problem that the preservative and the fixing agent are oxidized.
Even in such the method, however, there can not be overcome the problems that the preservative and fixing agent are susceptible to oxidation on the anode side by blowing air, and that reduction of the iron (III) ion takes place on the anode side. As a result, further improvements are desired.